Moving the bishop to d2 or f2 could also be considered.
5... g7g5 The best chance to create counterplay. Caruana undoubtedly had prepared this move in advance. 6. f4g5 Carlsen accepts the pawn sac. 6... e7e5 The idea with the sac is to control the center with the pawns. Next is d7-d5. 7. g2g4 A subtle move to gain access to the e4-square. 7... f5f4 A forced reaction.